Visual and cognitive processing in hemispatial neglect

Abstract

A number of theoretical issues can be investigated by examining patterns of eye movements in hemispatial neglect. For example, how the brain codes spatial information, how oculomotor behaviour relates to perception and awareness and what affects the allocation of spatial attention. These interesting questions will be outlined and discussed in a literature review presented in Chapter 1.

Experiment 1 involved collection of behavioural and eye movement data obtained from a chronic neglect patient (SS), stroke controls and older adult controls during completion of the three cancellation tasks from the Behavioural Inattention Test (Wilson, Cockburn, & Halligan, 1987). This revealed underlying deficits that were contributing to neglect. Not only was SS’s visual sampling of the neglected information limited, she also exhibited deficient and delayed processing of contralesional information when it was sampled.

Experiments 2 and 3, through newly developed cancellation tasks, examined whether different frames of reference for the coding of spatial information operate in neglect. The findings indicated that an allocentric (object-based) reference frame was not exhibited by patients with neglect when searching for specific targets letters, or clocks displaying specific times. Importantly, an egocentric reference frame based upon the position of gaze was able to account for the neglect behaviour exhibited. This suggests that many findings interpreted as evidence for allocentric neglect may be explained by the left side of the object falling to the left of the point of fixation, and therefore results from egocentric neglect.

Experiment 4 determined that the reference frame operating in neglect could be affected by task demands. As a processing deficit for contralesional information was shown in all the previous experiments reported in this thesis, Experiment 4 also aimed to investigate the stages of visual and cognitive processing that may be disrupted in neglect for contralesional information. The final chapter summarises the main findings and discussion of the main theoretical questions that have been outlined is presented. Conclusions are drawn with regards to these issues, which have previously been considered elusive functions of the brain (Buxbaum, 2006).

More information

Identifiers

Catalogue record

Export record